Hi, Ioan, I'm no EE, either - just a confirmed ME, but from the experience I've had, via hole diameter is dependant on 3 things: 1) current-carrying needs, 2) board thickness and 3) plating thickness. 1) If you know the power that the via hole has to carry, you can determine the cross-sectional area of the copper plating you need in the hole. 2) Adequate plating inside a hole depends partly on the plating process capability of your fab house and partly on the hole's aspect ratio (diameter to depth). Ask your fab house what their minimum hole diameter and aspect ratio is for achieving even plating thickness down the hole. From the thickness of your board, you can then determine whether you can use the minimum hole diameter as a baseline or diameter based on aspect ratio as a baseline. 3) Once you also know from your fab house the minimum hole plating thickness they can achieve, you have all the information you need to determine your finished hole sizes. Knowing the plating thickness and the X-sectional area of copper you need, you can simply calculate the length of copper required, which, of course will be the same as finished circumference of your finished hole. Divide it by Pi and you have the diameter. Obviously if your calculations come up with a hole diameter smaller than you fab house's minimum or, likewise, too large an aspect ratio, increasing the hole diameter won't do any harm - it only adds a margin of safety (which you should do yourself in any case). There is no maximum plating thickness, but bear in mind that you often get thicker plating on the board outer surfaces than you get in the holes. You don't want it to get too thick, or you run into over-etching problems, uneven coverage, etc., etc. You're safe enough with assuming a 1/2 oz (0.7 mils) min hole plating thickness for your calculations. Conversely, for the future, you can work out that if the current carrying requirements of a via are less than a certain value, you don't need to calculate hole diameters, since your fab house's minimum size will cope with it. Peter "Tempea, Ioan" <itempea@POSIT To: [log in to unmask] RON.QC.CA> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Sent by: Aero/ST Group) TechNet Subject: [TN] Via size <[log in to unmask] RG> 02/21/02 10:15 PM Please respond to "TechNet E-Mail Forum."; Please respond to "Tempea, Ioan" Hi technos, first I want to say to the Moonman "got your lean thing, as well as all the other documents you put there. Big thanks to you and Seth". Now, my question to the forum is: what are the rules in determining the diameter of vias? Has it anything to do with the current or the power? Can a power supply board, stepping down from 600V to 220V, have 0.018" vias? I know it sounds trivial, but I'm no EE. Thanks, Ioan --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------